Cetirizine is a potent H1 receptor antagonist that enters the body orally and rapidly binds to the histamine H1 receptor on the target cell membrane, blocking histamine from activating target cells. Cetirizine has no significant anticholinergic and anti-serotonin effects. At normal doses, it is not easy to penetrate the blood-brain barrier. This product can inhibit the histamine transmission in the initial stage of allergic reaction, reduce the migration activity of inflammatory cells and the release of transmitters in the late stage of allergic reaction, so it is also effective for allergic reactions in the late stage. This product is a highly selective H1 receptor antagonist, and has not been found to have adverse effects on cardiac electrical activity.